This column will change your life: Log your days and reap the benefits, says Oliver Burkeman

Last year, Nicholas Felton ate at 73 restaurants, read 2,400 pages in 14 books, walked an average of 3.13 miles a day, took 1,468 photographs and drank 408 beers, 30% of which were Stella Artois. We know this because the 31-year-old graphic designer, who lives in New York, recorded the data, crunched the numbers, and presented it online (at feltron.com) in a beautiful and oddly compelling "annual report". He's been doing this for several years, which prompts an obvious question: why? "Underlying curiosity, I guess," he told me. "One year, I calculated how many cups of coffee I drank, so I could tell how many fatal caffeine overdoses I'd have had if I'd had them all at once." He laughed at himself. "That made me happy," he said.

Felton is a pioneer of "personal informatics", the tracking and analysing of the daily minutiae of life. When I've mentioned self-monitoring here before, it's been in the context of the Hawthorne effect: the idea that the mere act of recording your spending, say, or your eating, will make you spend less, or eat more healthily. But personal informatics has far greater ambitions. Its adherents seek patterns in the data, order in the seeming chaos of the day: knowledge they can use to adjust their lives for the better.

Until recently, you'd have to have been an obsessive, or a narcissist, to invest the effort required to collect this information, but technology's changing that. (These days, being an obsessive narcissist is an optional extra.) The iPhone can record your movements using GPS; Google Health, with typical Orwellianness, promises to download data direct from heart-rate monitors or bathroom scales. And a host of sites offer to help identify patterns across your life: moodlog.org for your moods, trixietracker.com for your baby's sleeping and feeding habits, bedposted.com for your sex life ("Ever wonder how often you get busy?"), mon.thly.info and pmsbuddy.com for menstrual cycles, and daytum.com, which Felton co-founded, for tracking "anything you can count".

Identifying patterns has obvious benefits - cutting wasteful spending, reducing your carbon footprint - but subtler ones, too. Do you sleep worse after eating certain foods, or feel drained for days after socialising with certain people? For two weeks now, I've been receiving text messages from happyfactor.com, to which I reply with a description and rating of my mood; I can then examine my fluctuating happiness online. (Currently, in Britain, it works only on the O2 network.) Already I've learned that I'm at my most deflated and lethargic not right after lunch, as I'd believed, but about 4pm. So now I know when not to tackle challenging projects, or pilot passenger aircraft.

Felton sees his annual reports more as art than as self-improvement. But might his approach offer a new and valuable kind of self-knowledge? (Or largely new, anyway: tracking thoughts is already a cornerstone of cognitive therapy.) Our culture endlessly invites us to complexify our problems - to look first for deep-seated psychological issues, or to pick over our life experiences in search of explanations. But what if personal informatics revealed, for example, that your darkest moods always came on the days you forgot to eat breakfast? You might still want to explore the depths of your psyche. But you'd probably want to start eating breakfast more regularly first.

• This article was amended on Monday 30 March 2009. Happyfactor.com, not happytracker.com, is the website where you can track your happiness online. This has been corrected.